1st off, I main raider and have thrown hundreds of stunning taps but have not seen this much stamina drain on any character which is roughly 90%.
A Shugoki LA consumes a measly 1/16 stamina, and combined with headbutt, probably 1/4. A stunning tap would drain not over half any characters stamina. This seems to be connected the the Uninterruptable Stance, but as far as I know he only receives increased damage to health not stamina and only AFTER the armor was removed not during trade.
https://youtu.be/pSwXtsJEuVc